1. Field of the Invention
The present invention relates to a combustion control device for a gas turbine.
2. Background Art
A gas turbine typically includes a gas turbine body, a combustor, a compressor provided with inlet guide vanes (IGVs), and fuel flow rate control valves for controlling fuel supplies to fuel nozzles of the combustor. Such a gas turbine further includes a combustion control device for the gas turbine which is configured to control the fuel supplies to the fuel nozzles by controlling apertures of the fuel flow rate control valves, and an IGV control device configured to control apertures of the IGVs.
Moreover, the combustor may include one provided with multiple types of fuel nozzles, one provided with a main nozzle for premixed combustion and a pilot nozzle for diffuse combustion in order to reduce NOx at the time of high-load combustion and to achieve combustion stability at the time of low-load combustion, and one further provided with a top hat nozzle for premixed combustion in order to enhance NOx reduction and the like.
FIG. 39 is a block diagram showing an outline of a process flow in terms of a conventional gas turbine combustion control device. As shown in FIG. 39, the conventional gas turbine combustion control device is configured to set up a valve position command value (CSO) in the first place based on a power generator output command value transmitted from a central load dispatching center for managing power generator outputs in terms of multiple power generation facilities. Then, a pilot fuel flow rate control valve position command value (PLCSO), a top hat fuel flow rate (THCSO), and a main fuel flow rate control valve position command value (MACSO) are calculated based on this CSO, a function FX1 of the CSO and the PLCSO set up to obtain a given pilot ratio, a function FX2 of the CSO and the THCSO set up to obtain a given top hat ratio, and a calculation formula (MACSO=CSO−PLCSO−THCSO) for finding the MACSO. A fuel supply to the main nozzle, a fuel supply to the pilot nozzle, and a fuel supply to the top hat nozzle are controlled by regulating an aperture of a main fuel flow rate control valve, an aperture of a pilot flow rate control valve, and an aperture of a top hat control valve respectively based on these valve position command values, and thereby controlling the power generator output to match the power generator output command value. If an actual measurement value of the power generator output does not match the power generator output command value in this case, the gas turbine combustion control device adjusts the CSO based on deviations of these factors so as to achieve matching.
Meanwhile, when the gas turbine includes a combustor bypass valve for adjusting a bypass amount of compressed air to the combustor, the conventional combustion control device for the gas turbine calculates a combustor bypass valve position command value (BYCSO) based on a function (BYCSO=FX(MW/Pcs)) of a ratio (MW/FX(Pcs)) between a power generator output (a gas turbine output) MW and a function FX(Pcs) of a cylinder pressure Pcs and the BYCSO, as well as on a ratio (MW/FX(Pcs)) between an actual measurement value of the power generator output (the gas turbine output) MW and the function FX(Pcs) of an actual measurement value of the cylinder pressure Pcs as shown in FIG. 40. The bypass amount of the compressed air has been regulated by controlling an aperture of the combustor bypass valve based on this BYCSO. That is, in this case, a state of combustion of the gas turbine is regulated by performing the above-mentioned two control operations (i.e. the fuel flow rate control valve position control and the combustor bypass valve position control).
Of the following prior art documents, Patent Publication 1 discloses a pilot ratio automatic control device, Patent Publication 2 discloses a gas turbine fuel supply device, and Patent Publication 3 discloses a combustion control device, respectively.
(Patent Document 1) Japanese Unexamined Patent Publication No. 11(1999)-22490
(Patent Document 2) Japanese Unexamined Patent Publication No. 8(1996)-178290
(Patent Document 3) Japanese Unexamined Patent Publication No. 6(1994)-147484
The above-described conventional gas turbine combustion control device calculates the valve position command values (PLCSO, THCSO, and MACSO) of the respective fuel flow rate control valves directly by use of the CSO (the valve position command value). Specifically, the pilot ratio, the top hat ratio, and so forth are controlled as the functions of the CSO (the valve position command value). For this reason, the conventional gas turbine combustion control device has the following problems.    1. It is difficult to link the valve position command values (PLCSO, THCSO, and MACSO) of the respective fuel flow rate control valves with respective fuel gas ratios (the pilot ratio, the top hat ratio, and a main ratio). Moreover, relations of these factors are deviated in certain conditions.    2. When an intake-air temperature (an atmospheric temperature) changes in an operating state of a constant combustion gas temperature at an inlet of the gas turbine, such a change causes a variation in density of the intake gas and a change in the CSO, whereby the pilot ratio, the top hat ratio, and the main ratio are deviated. If the intake-air temperature changes as shown in an example of a relation between the combustion gas temperature TIT and the CSO relative to the variation in the intake-gas temperature in FIG. 41, the relation between the combustion gas temperature TIT and the CSO is deviated. Moreover, when the CSO is deviated, the PLCSO, the THCSO and the like are also deviated. As a consequence, the pilot ratio, the top hat ratio, and the like are deviated.    3. When a fuel gas temperature changes in the operating state at the constant gas temperature at the inlet of the gas turbine, such a change causes a variation in density of the fuel gas and a change in the CSO, whereby the pilot ratio, the top hat ratio, and the main ratio are deviated. If the fuel gas temperature changes as shown in an example of a relation between the combustion gas temperature TIT and the CSO relative to the variation in the fuel gas temperature in FIG. 42, the relation between the combustion gas temperature TIT and the CSO is deviated. Moreover, when the CSO is deviated, the PLCSO, the THCSO and the like are also deviated. As a consequence, the pilot ratio, the top hat ratio, and the like are also deviated.    4. When the performance of the gas turbine is deteriorated due to a drop in a capability of the compressor or the like in an operating state at a constant combustion gas temperature, such deterioration causes a variation in the CSO, whereby the pilot ratio, the top hat ratio, and the main ratio are deviated.    5. When the quality of the fuel gas (a calorific value of the fuel gas) changes in the operating state at the constant combustion gas temperature, such a change causes the variation in the CSO, whereby the pilot ratio, the top hat ratio, and the like are also deviated. If the calorific value of the fuel gas changes as shown in an example of a relation between the gas turbine output (the power generator output) and the CSO relative to the variation in the calorific value of the fuel gas temperature in FIG. 43, the relation between the gas turbine output (the power generator output) and the CSO is deviated. Moreover, when the CSO is deviated, the PLCSO, the THCSO and the like are also deviated. As a consequence, the pilot ratio, the top hat ratio, and the like are also deviated.
That is, the conventional gas turbine combustion control device is not configured to determine the valve position command values (PLCSO, THCSO, and MACSO) of the respective fuel flow rate control valves based on the respective fuel gas ratios (the pilot ratio, the top hat ratio, and the main ratio). Accordingly, it is difficult to link the valve position command values (PLCSO, THCSO, and MACSO) of the respective fuel flow rate control valves with the respective fuel gas ratios (the pilot ratio, the top hat ratio, and the main ratio). Moreover, the relations of these factors are deviated depending on the conditions.